Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A display device includes a plurality of pixels each including a
mechanical shutter. The display device electrically controls the position
of the mechanical shutter to provide image display. Each of the pixels
includes a pixel circuit for electrically controlling the position of the
mechanical shutter. The pixel circuit includes a first control electrode
and a second control electrode provided as a pair with respect to the
mechanical shutter; a first mean for applying a prescribed control
voltage to the first control electrode and the second control electrode
to put the mechanical shutter and the first control electrode or the
second control electrode into contact with each other; and a second mean
for, in a state where the mechanical shutter is at a stop, decreasing a
potential difference between the mechanical shutter and the first control
electrode or the second control electrode which is in contact with the
mechanical shutter.

Claims:

1. A display device, comprising a plurality of pixels each including a
mechanical shutter, the display device electrically controlling the
position of the mechanical shutter to provide image display, wherein:
each of the pixels includes a pixel circuit for electrically controlling
the position of the mechanical shutter; and the pixel circuit includes: a
first control electrode and a second control electrode provided as a pair
with respect to the mechanical shutter; a first mean for applying a
prescribed control voltage to the first control electrode and the second
control electrode to put the mechanical shutter and the first control
electrode or the second control electrode into contact with each other;
and a second mean for, in a state where the mechanical shutter is at a
stop, decreasing a potential difference between the mechanical shutter
and the first control electrode or the second control electrode which is
in contact with the mechanical shutter.

2. A display device, comprising a plurality of pixels each including a
mechanical shutter, the display device electrically controlling the
position of the mechanical shutter to provide image display, wherein:
each of the pixels includes a pixel circuit for electrically controlling
the position of the mechanical shutter; and the pixel circuit includes: a
first control electrode and a second control electrode provided as a pair
with respect to the mechanical shutter; a first mean for applying a
prescribed control voltage to the first control electrode and the second
control electrode to put the mechanical shutter and the first control
electrode or the second control electrode into contact with each other;
and a second mean for, in a state where the mechanical shutter is at a
stop, decreasing a potential difference between the mechanical shutter
and the second control electrode which is in contact with the mechanical
shutter.

3. A display device according to claim 1, wherein the second mean
decreases the potential difference between the mechanical shutter and the
first control electrode which is in contact with the mechanical shutter
or the potential difference between the mechanical shutter and the second
control electrode which is in contact with the mechanical shutter, by
controlling a shutter control voltage to be applied to the mechanical
shutter.

4. A display device according to claim 1, wherein the second mean
decreases the potential difference between the mechanical shutter and the
first control electrode which is in contact with the mechanical shutter
or the potential difference between the mechanical shutter and the second
control electrode which is in contact with the mechanical shutter.

5. A display device according to claim 1, wherein the pixel circuit
switches a state in which a control voltage lower than a shutter control
voltage to be applied to the mechanical shutter is applied to the first
control electrode and the second control electrode, and a state in which
a control voltage higher than the shutter control voltage to be applied
to the mechanical shutter is applied to the first control electrode and
the second control electrode, at a prescribed timing.

6. A display device, comprising: a plurality of pixels each including a
mechanical shutter; a signal line for inputting an image signal to each
of the pixels; a scanning line for inputting a scanning voltage to each
of the pixels; a first power supply line to be supplied with a first
power supply voltage; a second power supply line to be supplied with a
second power supply voltage; and a shutter voltage line connected to the
mechanical shutter and to be supplied with a shutter control voltage;
wherein: the display device electrically controls the position of the
mechanical shutter to provide image display; each of the pixels includes
a pixel circuit for electrically controlling the position of the
mechanical shutter; the pixel circuit includes: a first control electrode
and a second control electrode provided as a pair with respect to the
mechanical shutter; an input transistor which includes a current terminal
having one end connected to the signal line, the input transistor having
a gate connected to the scanning line; a storage capacitance having one
end connected to the other end of the current terminal of the input
transistor and having the other end connected to the first power supply
line, the storage capacitance storing a voltage received by the input
transistor; a first transistor of a first conductivity type which
includes a current terminal having one end connected to the second power
supply line and the other end connected to the second control electrode,
the first transistor having a gate to which the voltage stored by the
storage capacitance is input; a second transistor of the first
conductivity type which includes a current terminal having one end
connected to the second power supply line and the other end connected to
the first control electrode, the second transistor having a gate
connected to the second control electrode; a third transistor of a second
conductivity type which includes a current terminal having one end
connected to the first power supply line and the other end connected to
the second control electrode, the third transistor having a gate to which
the voltage stored by the storage capacitance is input; and a fourth
transistor of the second conductivity type which includes a current
terminal having one end connected to the first power supply line and the
other end connected to the first control electrode, the fourth transistor
having a gate connected to the second control electrode; and a voltage
level of the shutter control voltage is changed at a prescribed timing to
put the mechanical shutter and the first control electrode or the second
control electrode into contact with each other, and in a state where the
mechanical shutter is at a stop, a potential difference between the
mechanical shutter and the first control electrode or the second control
electrode which is in contact with the mechanical shutter is decreased.

7. A display device, comprising: a plurality of pixels each including a
mechanical shutter; a signal line for inputting an image signal to each
of the pixels; a scanning line for inputting a scanning voltage to each
of the pixels; a first power supply line to be supplied with a first
power supply voltage; a second power supply line to be supplied with a
second power supply voltage; and a shutter voltage line connected to the
mechanical shutter and to be supplied with a shutter control voltage;
wherein: the display device electrically controls the position of the
mechanical shutter to provide image display; each of the pixels includes
a pixel circuit for electrically controlling the position of the
mechanical shutter; the pixel circuit includes: a first control electrode
and a second control electrode provided as a pair with respect to the
mechanical shutter; an input transistor which includes a current terminal
having one end connected to the signal line, the input transistor having
a gate connected to the scanning line; a storage capacitance having one
end connected to the other end of the current terminal of the input
transistor and having the other end connected to the first power supply
line, the storage capacitance storing a voltage received by the input
transistor; a first transistor of a first conductivity type which
includes a current terminal having one end connected to the second power
supply line and the other end connected to the second control electrode,
the first transistor having a gate to which the voltage stored by the
storage capacitance is input; a second transistor of the first
conductivity type which includes a current terminal having one end
connected to the first power supply line and the other end connected to
the second control electrode, the second transistor having a gate
connected to the second control electrode; a third transistor of a second
conductivity type which includes a current terminal having one end
connected to the second power supply line and the other end connected to
the first control electrode, the third transistor having a gate to which
the voltage stored by the storage capacitance is input; and a fourth
transistor of the second conductivity type which includes a current
terminal having one end connected to the first power supply line and the
other end connected to the first control electrode, the fourth transistor
having a gate connected to the second control electrode; and a voltage
level of the first power supply voltage or a voltage level of the second
power supply voltage is changed at a prescribed timing to put the
mechanical shutter and the first control electrode or the second control
electrode into contact with each other, and in a state where the
mechanical shutter is at a stop, a potential difference between the
mechanical shutter and the first control electrode or the second control
electrode which is in contact with the mechanical shutter is decreased.

8. A display device according to claim 6, further comprising a transfer
transistor which includes a current terminal having one end connected to
the first control electrode and the other end connected to the one end of
the storage capacitance, the transfer transistor having a gate to which a
transfer control signal is input.

9. A display device, comprising: a plurality of pixels each including a
mechanical shutter; a signal line for inputting an image signal to each
of the pixels; a scanning line for inputting a scanning voltage to each
of the pixels; a first power supply line to be supplied with a first
power supply voltage; a second power supply line to be supplied with a
second power supply voltage; a shutter voltage line connected to the
mechanical shutter and to be supplied with a shutter control voltage; a
reset line to be supplied with a reset voltage; and a control line to be
supplied with a control voltage; wherein: the display device electrically
controls the position of the mechanical shutter to provide image display;
each of the pixels includes a pixel circuit for electrically controlling
the position of the mechanical shutter; the pixel circuit includes: a
first control electrode and a second control electrode provided as a pair
with respect to the mechanical shutter; an input transistor which
includes a current terminal having one end connected to the signal line,
the input transistor having a gate connected to the scanning line; a
storage capacitance having one end connected to the other end of the
current terminal of the input transistor and having the other end
connected to the shutter voltage line, the storage capacitance storing a
voltage received by the input transistor; a first transistor of a first
conductivity type which includes a current terminal having one end
connected to the second power supply line and the other end connected to
the first control electrode, the first transistor having a gate connected
to the reset line; and a second transistor of a second conductivity type
which includes a current terminal having one end connected to the first
power supply line and the other end connected to the first control
electrode, the second transistor having a gate to which the voltage
stored by the storage capacitance is input; the second control electrode
is connected to the control line; and a voltage level of the shutter
control voltage is changed at a prescribed timing to put the mechanical
shutter and the first control electrode or the second control electrode
into contact with each other, and in a state where the mechanical shutter
is at a stop, a potential difference between the mechanical shutter and
the first control electrode or the second control electrode which is in
contact with the mechanical shutter is decreased.

10. A display device, comprising: a plurality of pixels each including a
mechanical shutter; a signal line for inputting an image signal to each
of the pixels; a scanning line for inputting a scanning voltage to each
of the pixels; a first power supply line to be supplied with a first
power supply voltage; a second power supply line to be supplied with a
second power supply voltage; a shutter voltage line connected to the
mechanical shutter and to be supplied with a shutter control voltage; a
reset line to be supplied with a reset voltage; and a control line to be
supplied with a control voltage; wherein: the display device electrically
controls the position of the mechanical shutter to provide image display;
each of the pixels includes a pixel circuit for electrically controlling
the position of the mechanical shutter; the pixel circuit includes: a
first control electrode and a second control electrode provided as a pair
with respect to the mechanical shutter; an input transistor which
includes a current terminal having one end connected to the signal line,
the input transistor having a gate connected to the scanning line; a
storage capacitance having one end connected to the other end of the
current terminal of the input transistor and having the other end
connected to the shutter voltage line, the storage capacitance storing a
voltage received by the input transistor; a first transistor of a first
conductivity type which includes a current terminal having one end
connected to the second power supply line and the other end connected to
the first control electrode, the first transistor having a gate connected
to the reset line; and a second transistor of a second conductivity type
which includes a current terminal having one end connected to the first
power supply line and the other end connected to the first control
electrode, the second transistor having a gate to which the voltage
stored by the storage capacitance is input; the second control electrode
is connected to the control line; and a voltage level of the shutter
control voltage is changed at a prescribed timing to put the mechanical
shutter and the first control electrode or the second control electrode
into contact with each other, and in a state where the mechanical shutter
is at a stop, a potential difference between the mechanical shutter and
the second control electrode which is in contact with the mechanical
shutter is decreased.

11. A display device according to claim 9, further comprising: a third
transistor of the first conductivity type which is connected between the
first transistor and the first control electrode; and a fourth transistor
of the second conductivity type which is connected between the second
transistor and the first control electrode; wherein a gate of the third
transistor and a gate of the fourth transistor are to be supplied with a
prescribed voltage.

12. A display device according to claim 6, wherein: the first and second
transistors are each a p-type transistor; the third and fourth
transistors are each an n-type transistor; and the second power supply
voltage has a higher potential than that of first power supply voltage.

13. A display device according to claim 6, wherein the first through
fourth transistors each include a semiconductor layer formed of a
polycrystalline silicon film.

14. A display device according to claim 6, wherein the first through
fourth transistors each include a semiconductor layer formed of an
amorphous silicon film.

15. A method for driving a display device, wherein: the display device
includes a plurality of pixels each including a mechanical shutter; each
of the pixels includes a pixel circuit for electrically controlling the
position of the mechanical shutter; the pixel circuit includes a first
control electrode and a second control electrode provided as a pair with
respect to the mechanical shutter; and the display device electrically
controls the position of the mechanical shutter to provide image display,
the driving method comprising applying a prescribed control voltage to
the first control electrode and the second control electrode to put the
mechanical shutter and the first control electrode or the second control
electrode into contact with each other; and in a state where the
mechanical shutter is at a stop, decreasing a potential difference
between the mechanical shutter and the first control electrode or the
second control electrode which is in contact with the mechanical shutter.

16. A method for driving a display device, wherein: the display device
includes a plurality of pixels each including a mechanical shutter; each
of the pixels includes a pixel circuit for electrically controlling the
position of the mechanical shutter; the pixel circuit includes a first
control electrode and a second control electrode provided as a pair with
respect to the mechanical shutter; and the display device electrically
controls the position of the mechanical shutter to provide image display,
the driving method comprising applying a prescribed control voltage to
the first control electrode and the second control electrode to put the
mechanical shutter and the first control electrode or the second control
electrode into contact with each other; and in a state where the
mechanical shutter is at a stop, decreasing a potential difference
between the mechanical shutter and the second control electrode which is
in contact with the mechanical shutter.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priority
from the prior Japanese Patent Application No. 2011-282643, filed on Dec.
26, 2011, the entire contents of which are incorporated herein by
reference.

FIELD

[0002] The present invention relates to a display device and a method for
driving the same, and specifically to a technology effectively applicable
to a pixel circuit of an image display device for electrically
controlling the position of a mechanical shutter to provide image
display.

BACKGROUND

[0003] A method of using an image display device for electrically
controlling the position of a mechanical shutter to provide image display
(hereinafter, referred to as a "movable shutter-type image display
device") is described in US 2008/0174532.

[0005] Hereinafter, the conventional movable shutter-type image display
device will be described with reference to FIG. 16.

[0006] Each pixel circuit 213 includes a signal line 206. The signal line
206 and a signal storage capacitance 204 are connected to each other by a
signal transfer switch 205.

[0007] The signal storage capacitance 204 is also connected to a gate of
an n-type MOS transistor 203 for shutter negative voltage write. A drain
of the n-type MOS transistor 203 for shutter negative voltage write is
connected to a drain of a p-type MOS transistor 202 for shutter positive
voltage write via a cascode n-type MOS transistor 216 and a cascode
p-type MOS transistor 215.

[0008] Each pixel includes a dual actuator shutter assembly 201 connected
to a shutter voltage line 211. One of two control electrodes of the dual
actuator shutter assembly 201 is connected to the drain of the n-type MOS
transistor 203 for shutter negative voltage write via the cascode n-type
MOS transistor 216. The other control electrode is connected to a control
electrode voltage line 209.

[0009] The other end of the signal storage capacitance 204 is connected to
the shutter voltage line 211. A source of the n-type MOS transistor 203
for shutter negative voltage write is connected to an nMOS source voltage
line 212 for shutter negative voltage write.

[0010] A gate and the drain of the p-type MOS transistor 202 for shutter
positive voltage write are respectively connected to a pMOS gate voltage
line 207 for shutter positive voltage write and a positive voltage line
208. A gate of the cascode n-type MOS transistor 216 and a gate of the
cascode p-type MOS transistor 215 are connected to a cascode gate voltage
line 217. A gate of the signal transfer switch 205 is connected to a
scanning line 210.

[0011] The dual actuator shutter assembly 201 is provided to face an
opening in a light blocking surface. This image display device includes a
plurality of such pixel circuits 213 arrayed in a matrix.

[0012] Now, an operation of the conventional movable shutter-type image
display device will be described.

[0013] An image signal voltage written to the signal line 206 is stored on
the signal storage capacitance 204 via the signal transfer switch 205 by
scanning the scanning lines 210 sequentially.

[0014] Then, after the scanning operation for writing an image signal
voltage on the signal storage capacitances 204 of all the pixels is
finished, each pixel performs amplified write of an image signal to one
of the control electrodes of the dual actuator shutter assembly 201,
based on the written image signal voltage. Namely, in all the pixels, the
pMOS gate voltage line 207 for shutter positive voltage write is put into
a low voltage state for a prescribed time period, so that the p-type MOS
transistor 202 for shutter positive voltage write is put into an ON state
for this period. Thus, one of the control electrodes of the dual actuator
shutter assembly 201 is precharged with a prescribed positive voltage,
which has been applied to the positive voltage line 208.

[0015] Next, the nMOS source voltage line 212 for shutter negative voltage
write is put into a low voltage state for a prescribed time period. For
this period, only in a pixel which includes the signal storage
capacitance 204 having a high voltage as an image signal voltage written
therein, the n-type MOS transistor 203 for shutter negative voltage write
is put into an ON state. As a result, the voltage of one of the control
electrodes of the dual actuator shutter assembly 201 is re-rewritten with
a prescribed low voltage applied to the nMOS source voltage line 212 for
shutter negative voltage write.

[0016] In a pixel which includes the signal storage capacitance 204 having
a low voltage as an image signal voltage written therein, the n-type MOS
transistor 203 for shutter negative voltage write is kept in an OFF state
for the above-mentioned period. Therefore, the voltage of one of the
control electrodes of the dual actuator shutter assembly 201 is kept in
the state of being precharged at the prescribed positive voltage.

[0017] In this manner, amplified write of an image signal is performed on
one of the control electrodes of the dual actuator shutter assembly 201.
In parallel with this, a voltage applied to the control electrode voltage
line 209 is controlled, so that the dual actuator shutter assembly 201
can be electrostatically operated to be opened or closed. The opening
provided in the light blocking surface of the dual actuator shutter
assembly 201 is opened or closed in this manner, so that the amount of
transmitted light is controlled. Thus, the image display device can
display an image corresponding to the written image signal voltage on the
pixel matrix.

[0018] In the above-described operation, the cascode n-type MOS transistor
216 and the cascode p-type MOS transistor 215 are provided in order to
protect the p-type MOS transistor 202 for shutter positive voltage write
and the n-type MOS transistor 203 for shutter negative voltage write
against write of a high drain voltage which may spoil the reliability
life thereof.

[0019] It was found that in a movable shutter-type image display device, a
control fault of a mechanical shutter which reduces the life of the
device is caused by an adhesive force caused between the shutter
electrode and the control electrode.

[0020] This will be described with reference to FIG. 6. FIG. 6 provides
schematic views of a shutter electrode 20 and a control electrode 21
provided in each of pixels in a movable shutter-type image display
device. An insulating film 50 of alumina or silicon nitride is provided
around the electrodes.

[0021] FIG. 6(a) shows that the shutter electrode 20 is electrostatically
attracted to the control electrode 21. A voltage of, for example, 25V is
applied between the electrodes. At this point, a prescribed electric
field is generated in the insulating film 50 located between the
electrodes, and thus a leak current is generated due to Poole-Frankel or
Fowler-Nordheim injection current.

[0022] Which of the current injection mechanisms mainly acts is determined
by the quality of the film, electric field, temperature or the like. For
example, in the case where the shutter electrode 20 is supplied with a
negative voltage and the control electrode 21 is supplied with a positive
voltage, the generated leak current is defined as electron injection
directed from the shutter electrode 20 toward the control electrode 21.
It should be noted that the insulating film 50 located between the
electrodes has a contact interface and a great number of electron trap
levels are existent around the contact interface.

[0023] Electrons released from the insulating film 50 on the shutter
electrode 20 side are concentrated in tiny convexed portions on the
insulating film, and therefore the influence of the electron trap is
small. By contrast, on the control electrode 21 side, injected electrons
are dispersed in a large area of the interface of the insulating film 50,
and therefore a great number of electrons are trapped at the electron
trap levels. This is shown in FIG. 6(b).

[0024] FIG. 6(c) shows a state where no voltage is applied between the
electrodes after the state of FIG. 6(b). Even when there is no voltage
applied anymore, electrons, once trapped, stay at the interface of the
insulating film 50 for a relatively long period. Even when a negative
electrode is kept applied to the shutter electrode 20 and a positive
electrode is kept applied to the control electrode 21 in order to close
the electrodes, the residual charges decrease the potential of the
positive electrode. As a result, the control on the shutter performed by
use of electrostatic attraction is destabilized. As a result, the life of
the mechanical shutter or the life of the display device may be reduced.

[0025] The present invention for solving these problems of the
conventional art has an object of providing a technology capable of, in a
movable shutter-type image display device, significantly decreasing the
amount of trapped electrons (charges) caused by a leak current to
alleviate the control fault of the mechanical shutter and thus to
significantly extend the life of the display.

[0026] The foregoing and the other objects and novel features of the
present invention will be made clear by the description in this
specification and the attached drawings.

SUMMARY

[0027] Representative subject matter of the invention disclosed in this
application is as follows.

[0028] In order to solve the above-described problems, the present
invention is directed to a display device, comprising a plurality of
pixels each including a mechanical shutter, the display device
electrically controlling the position of the mechanical shutter to
provide image display, wherein each of the pixels includes a pixel
circuit for electrically controlling the position of the mechanical
shutter; and the pixel circuit includes a first control electrode and a
second control electrode provided as a pair with respect to the
mechanical shutter; a first mean for applying a prescribed control
voltage to the first control electrode and the second control electrode
to put the mechanical shutter and the first control electrode or the
second control electrode into contact with each other; and a second mean
for, in a state where the mechanical shutter is at a stop, decreasing a
potential difference between the mechanical shutter and the first control
electrode or the second control electrode which is in contact with the
mechanical shutter.

[0029] The present invention is also directed to a display device,
comprising a plurality of pixels each including a mechanical shutter, the
display device electrically controlling the position of the mechanical
shutter to provide image display, wherein each of the pixels includes a
pixel circuit for electrically controlling the position of the mechanical
shutter; and the pixel circuit includes a first control electrode and a
second control electrode provided as a pair with respect to the
mechanical shutter; a first mean for applying a prescribed control
voltage to the first control electrode and the second control electrode
to put the mechanical shutter and the first control electrode or the
second control electrode into contact with each other; and a second mean
for, in a state where the mechanical shutter is at a stop, decreasing a
potential difference between the mechanical shutter and the second
control electrode which is in contact with the mechanical shutter.

BRIEF DESCRIPTION OF DRAWINGS

[0030] FIG. 1 is a circuit diagram showing a pixel circuit of a movable
shutter-type image display device in Example 1 according to the present
invention.

[0031] FIG. 2 is a block diagram showing a schematic structure of the
movable shutter-type image display device in Example 1 according to the
present invention.

[0032] FIG. 3 is a cross-sectional view showing a cross-sectional
structure of a pixel area of the movable shutter-type image display
device in Example 1 according to the present invention.

[0046] Hereinafter, examples of the present invention will be described
with reference to the drawings.

[0047] In the drawings provided to explain the examples, elements having
identical functions will bear identical reference numerals, and the same
descriptions will be omitted. The following examples do not limit the
scope or interpretation of the claims of the present invention.

Example 1

[0048] FIG. 1 is a circuit diagram showing a pixel circuit of a movable
shutter-type image display device in Example 1 according to the present
invention.

[0049] A pixel circuit 23 in this example is a CMOS circuit, and includes
p-type MOS transistors 2 and 14 connected between a power supply line 7
supplied with a VDD voltage and a power supply line 12 supplied with a
GND voltage, and n-type MOS transistors 3 and 15.

[0050] Each pixel circuit 23 includes a signal line 6, and the signal line
6 and a signal storage capacitance (hereinafter, referred to as a
"storage capacitance") 4 are connected to each to other by a signal
transfer switch (input transistor according to the present invention) 5,
which is an n-type MOS transistor.

[0051] The storage capacitance 4 is also connected to a source (or a
drain) of a signal transfer switch (transfer transistor) according to the
present invention) 13, which is an n-type MOS transistor. The drain (or
the source) of the signal transfer switch 13 is connected to a gate of
the p-type MOS transistor 2 and a gate of the n-type MOS transistor 3.
The other end of the storage capacitance 4 is connected to the power
supply line 12, and a gate of the signal transfer switch 5 is connected
to an update line 8.

[0052] The gate of the p-type MOS transistors 2 and the gate of the n-type
MOS transistor 3 are connected to one of control electrodes 22 of a
mechanical shutter, and a gate of the p-type MOS transistor 14 and a gate
of the n-type MOS transistor 15 are connected to the other control
electrode of the mechanical shutter. The shutter electrode 20 is
connected to a shutter voltage line 11.

[0053] As described later with reference to FIG. 3, the mechanical shutter
is provided to face an opening in a light blocking surface.

[0054] FIG. 2 is a block diagram showing a schematic structure of the
movable shutter-type image display device in Example 1 according to the
present invention.

[0055] In the movable shutter-type image display device shown in FIG. 2, a
plurality of the pixel circuits 23 shown in FIG. 1 are arrayed
two-dimensionally, and each pixel circuit 23 acts as a pixel. A scanning
line 10 is provided for each row and is connected to a scanning circuit
25.

[0056] The signal line 6 is provided for each column and is connected to
an image signal voltage write circuit 24. The power supply lines 7 and
12, the update line 8, and the shutter voltage line 11 are provided
commonly to the pixels, and are connected to a control electrode driving
circuit 26.

[0057] FIG. 2 shows a display area as including the pixels in a matrix of
4×3 for the sake of simplicity, but obviously, the technological
philosophy of the present invention does not specifically limit the
number of pixels.

[0058] Now, a cross-sectional structure of a pixel area of the movable
shutter-type image display device in this example will be described.

[0059] FIG. 3 is a cross-sectional view showing a cross-sectional
structure of the pixel area of the movable shutter-type image display
device in Example 1 according to the present invention.

[0060] As shown in FIG. 3, a polycrystalline silicon thin film transistor
is provided on a glass substrate 39. The polycrystalline silicon thin
film transistor includes a polycrystalline silicon thin film 31,
polycrystalline silicon thin films 30 and 32 doped with a high
concentration n-type impurity, a gate insulating film 33, and a gate
electrode 35, a source electrode 37 and a drain electrode 36 which are
formed of a high melting point metal material.

[0061] The following elements are further provided on the glass substrate
39 while an insulating protective film 34 is held between the
above-mentioned elements and the following elements: a shutter voltage
line 11 and a drain electrode 40 (e.g., drain of the n-type MOS
transistor 15) which are formed of Al like the source electrode 37 and
the drain electrode 36. These elements are covered with a protective film
38 including a plurality of layers of silicon nitride and an organic
material.

[0062] On the protective film 38, a dual actuator shutter assembly 1
including the shutter electrode 20 and control electrodes 21 and 22 is
provided. The shutter electrode 20 is connected to the shutter voltage
line 11, the drain electrode 36 is connected to the control electrode 22,
and the drain electrode 40 is connected to the control electrode 21, via
respective contact holes. The shutter electrode 20 and the two control
electrodes 21 and 22 are covered with an insulating film so as not to be
short-circuited when contacting each other.

[0063] The position of the shutter electrode 20 is controlled by an
electric field which is varied by the relationship between the voltage
applied to the shutter electrode 20 and the voltage applied to the
control electrodes 20 and 21. For this reason, FIG. 3 also shows the
movable range of the shutter electrode 20.

[0064] Although not shown in FIG. 3, other transistors provided in the
pixel circuit 23 are also polycrystalline silicon thin film transistors.
These polycrystalline silicon thin film transistors can be produced by
use of a known excimer laser annealing process or the like.

[0065] At a position facing the glass substrate 39 with the shutter
electrode 20 located therebetween, a light guide plate 47 including a
light source 42 is provided. The light source 42 includes independent LED
light sources of three colors of R (red), G (green) and B (blue).

[0066] On both of two surfaces of the light guide plate 47, reflective
films 46 and 48 are provided respectively, and a black film 49 is
provided on the reflective film 48. The reflective films 46 and 48 are
metal films of Ag, Al or the like. The black film 49 may be formed of a
metal oxide film, a polyimide resin or the like which has pigment
particles of carbon black, titanium black or the like dispersed therein
appropriately.

[0067] As shown in FIG. 3, the reflective film 48 and the black film 49
have an opening at a position corresponding to the shutter electrode 20.
A part of light 41 emitted from the light source 42 and propagated in the
light guide plate 47 is output through the opening. The black film 49 is
provided in order to prevent reflection of external light.

[0068] Now, with reference to FIG. 4 and FIG. 5, an operation of the
movable shutter-type image display device in this example will be
described.

[0069] FIG. 4 and FIG. 5 are each an operation timing diagram of the
movable shutter-type image display device in this example according to
the present invention. In FIG. 4 and FIG. 5, regarding a shutter control
voltage on the shutter voltage line (shutter line) 11, a scanning voltage
on the scanning line (gate line) 10, a transfer control signal on the
update line 8, and a power supply voltage on the power supply line
(actuate line) 7, the horizontal axis represents the time and the
vertical axis represents the level of the voltage. Regarding the shutter
electrode 20 at the bottom, FIG. 4 and FIG. 5 show the position of the
shutter electrode 20 with respect to the control electrodes 21 and 22.

[0070] The shutter voltage line 11 has a voltage of 0V in FIG. 4 and has a
high Vdrive voltage (e.g., 25V) in FIG. 5. This corresponds to an
inversion (polarity inversion) operation of the driving voltage of the
mechanical shutter.

[0071] The image display device in this example represents full-color
8-bit gradation by an opened/closed state of the shutter. For realizing
this, the following PMW (Pulse Width Modulation) driving is performed.
One frame is divided into at least 24 (=8×RGB) frames, and light
emission from the light source 42 is time-weighted for each sub frame.
The light emission to the outside is controlled by opening or closing the
shutter electrode 20. During the driving, polarity inversion driving is
performed at an interval of a prescribed number of sub frames in order to
avoid deterioration of the electrodes of the mechanical shutter.

[0072] First, with reference to FIG. 4, an operation of the pixel circuit
of the movable shutter-type image display device in this example in the
state of "polarity inversion: shutter=low voltage" will be described.

[0073] Until time t1, the scanning line 10 is sequentially supplied with
scanning voltages and an image signal is written in the storage
capacitance 4.

[0074] Next, at time t1, the power supply voltage on the power supply line
7 becomes from a level of Vdrive (e.g., 25V) to 0V, and the shutter
control voltage on the shutter voltage line 11 becomes from a level of
Vrelease1 (e.g., 10V) to 0V.

[0075] Next, at time t2, the transfer control signal on the update line 8
becomes High (hereinafter, referred to as "H level"), and thus the signal
transfer switch 13 is turned ON. As a result, a signal is input to an
SRAM circuit formed of the p-type MOS transistors 2 and 14 and the n-type
MOS transistors 3 and 15.

[0076] At time t3, the power supply voltage of the power supply line 7 is
raised to a level of Vlatch, and thus an image signal is latched by the
SRAM circuit.

[0077] Then, at time t4, the transfer control signal on the update line 8
becomes Low (hereinafter, referred to as "L level"), and thus the signal
transfer switch 13 is turned OFF.

[0078] At time t5, the power supply voltage on the power supply line 7 is
raised to a level of Vdrive (e.g., 25V), and thus the shutter electrode
20 is driven.

[0079] In an initial state, the shutter electrode 20 is in contact with
either the control electrode 21 or 22. After time t1, as a result of the
power supply voltage on the power supply line 7 becoming 0V, the shutter
electrode 20 is moved to an intermediate position. Then, at time t5, the
shutter electrode 20 starts moving toward either the control electrode 21
or 22. At this point, the shutter electrode 20 is supplied with a voltage
of 0V. The control electrode on a high voltage side is supplied with a
Vdrive voltage (e.g., 25V), whereas the control electrode on a low
voltage side is supplied with a voltage of 0V.

[0080] Then, at time t6, at the timing when the shutter electrode 20 stops
moving, the shutter control voltage on the shutter voltage line 11
becomes a level of Vrelease1 (e.g., 10V). As a result, the potential
difference between the shutter electrode 20 and the control electrode on
the high voltage side is decreased from 25V to 15V. At this point, the
shutter electrode 20 is already at a stop. Therefore, there is no
influence on the shutter characteristics even though the applied voltage
is decreased.

[0081] Now, with reference to FIG. 5, an operation of the pixel circuit of
the movable shutter-type image display device in this example in the
state of "polarity inversion: shutter=high voltage" will be described.

[0082] Until time t1, the scanning line 10 is sequentially supplied with
scanning voltages and an image signal is written in the storage
capacitance 4.

[0083] Next, at time t1, the power supply voltage on the power supply line
7 becomes from a level of Vdrive (e.g., 25V) to 0V, and the shutter
control voltage on the shutter voltage line 11 becomes from a level of
Vrelease2 (e.g., 15V) to a level of Vdrive (e.g., 25V).

[0084] Next, at time t2, the transfer control signal on the update line 8
becomes H level, and thus the signal transfer switch 13 is turned ON. As
a result, a signal is input to the SRAM circuit formed of the p-type MOS
transistors 2 and 14 and the n-type MOS transistors 3 and 15.

[0085] At time t3, the power supply voltage of the power supply line 7 is
raised to a level of Viatch, and thus an image signal is latched by the
SRAM circuit.

[0086] Then, at time t4, the transfer control signal on the update line 8
becomes L level, and thus the signal transfer switch 13 is turned OFF.

[0087] At time t5, the power supply voltage on the power supply line 7 is
raised to a level of Vdrive (e.g., 25V), and thus the shutter electrode
20 is driven.

[0088] In an initial state, the shutter electrode 20 is in contact with
either the control electrode 21 or 22. At time t5, the shutter electrode
20 starts moving toward either the control electrode 21 or 22. At this
point, the shutter electrode 20 is supplied with a Vdrive voltage (e.g.,
25V). The control electrode on the high voltage side is supplied with a
Vdrive voltage (e.g., 25V), whereas the control electrode on the low
voltage side is supplied with a voltage of 0V.

[0089] Then, at time t6, at the timing when the shutter electrode 20 stops
moving, the shutter control voltage on the shutter voltage line 11
becomes a level of Vrelease2 (e.g., 15V). As a result, the potential
difference between the shutter electrode 20 and the control electrode on
the low voltage side is decreased from 25V to 15V. At this point, the
shutter electrode 20 is already at a stop. Therefore, there is no
influence on the shutter characteristics even though the applied voltage
is decreased.

[0090] The operation in FIG. 5 is opposite to the operation in FIG. 4 in
the high/low relationship regarding the shutter control voltage on the
shutter voltage line 11. For this reason, the operation of the shutter 20
is different, but the basic operating principle is the same.

[0091] As described above, in this example, until the shutter electrode 20
contacts either the control electrode 21 or 22, the potential difference
between the voltages applied to the electrodes is 25V as by the
conventional art. After the electrodes contact each other, the potential
difference between the voltages applied to the electrodes is decreased to
15V.

[0092] A leak current between the electrodes is in proportion to the
voltage applied between the electrodes (Poole-Frankel injection current)
or is an exponential function of the voltage applied between the
electrodes (Fowler-Nordheim injection current). Therefore, the leak
current heavily relies on the voltage.

[0093] The leak current is generated after the electrodes contact each
other. By decreasing the potential difference between the voltages
applied to the electrodes from 25V to 15V after the electrodes contact
each other, the amount of trapped electrons (charges) caused by the leak
current can be decreased significantly. As a result, the control fault of
the mechanical shutter can be alleviated, and the life of the display
device can be extended significantly.

[0094] The control of the shutter electrode (operation of moving the
shutter electrode toward the control electrode 21 or toward the control
electrode 22) uses the potential difference of 25V. Therefore, even
though the applied voltage is decreased, there is no influence on the
shutter characteristics.

[0095] In the above description, until the shutter electrode 20 contacts
either the control electrode 21 or 22, the potential difference between
the voltages applied to the electrodes is 25 V as by the conventional
art. After the electrodes contact each other, the potential difference
between the voltages applied to the electrodes is decreased to 15V. As
long as the potential difference between the voltages applied to the
electrodes is between 10V and 15V, substantially the same function and
effect are provided.

Example 2

[0096] A movable shutter-type image display device and a pixel circuit in
this example have substantially the same structure as that in Example 1
described above, and will not be described again.

[0097] FIG. 7 and FIG. 8 are each an operation timing diagram of the
movable shutter-type image display device in this example according to
the present invention. FIG. 7 and FIG. 8 respectively correspond to FIG.
4 and FIG. 5 described above. In FIG. 7 and FIG. 8, regarding the shutter
control voltage on the shutter voltage line (shutter line) 11, the power
supply on the power supply line (low line) 12, the scanning voltage on
the scanning line (gate line) 10, the transfer control signal on the
update line 8, and the power supply voltage on the power supply line
(actuate line) 7, the horizontal axis represents the time and the
vertical axis represents the level of the voltage. Regarding the shutter
electrode 20 at the bottom, FIG. 7 and FIG. 8 show the position of the
shutter electrode 20 with respect to the control electrodes 21 and 22.

[0098] In this example, the power supply voltage on the power supply line
7, instead of the shutter control voltage on the shutter voltage line 11,
is varied to decrease the voltage applied to the control voltages 21 and
22 from the level of the Vdrive voltage to the level of Vrelease3.

[0099] First, with reference to FIG. 7, an operation of the pixel circuit
of the movable shutter-type image display device in this example in the
state of "polarity inversion: shutter=low voltage" will be described. In
FIG. 7, the shutter control voltage on the shutter voltage line 11 is 0V.

[0100] Until time t1, the scanning line 10 is sequentially supplied with
scanning voltages and an image signal is written in the storage
capacitance 4.

[0101] Next, at time t1, the power supply voltage on the power supply line
7 becomes from a level of Vrelease3 (e.g., 15V) to 0V.

[0102] Next, at time t2, the transfer control signal on the update line 8
becomes H level, and thus the signal transfer switch 13 is turned ON. As
a result, a signal is input to the SRAM circuit formed of the p-type MOS
transistors 2 and 14 and the n-type MOS transistors 3 and 15.

[0103] At time t3, the power supply voltage on the power supply line 7 is
raised to a level of Vlatch, and thus an image signal is latched by the
SRAM circuit.

[0104] Then, at time t4, the transfer control signal on the update line 8
becomes L level, and thus the signal transfer switch 13 is turned OFF.

[0105] At time t5, the power supply voltage on the power supply line 7 is
raised to a level of Vdrive (e.g., 25V), and thus the shutter electrode
20 is driven.

[0106] In an initial state, the shutter electrode 20 is in contact with
either the control electrode 21 or 22. After time t1, as a result of the
power supply voltage on the power supply line 7 becoming 0V, the shutter
electrode 20 is moved to an intermediate position. Then, at time t5, the
shutter electrode 20 starts moving toward either the control electrode 21
or 22. At this point, the shutter electrode 20 is supplied with a voltage
of 0V. The control electrode on the high voltage side is supplied with a
Vdrive voltage (e.g., 25V), whereas the control electrode on the low
voltage side is supplied with a voltage of 0V.

[0107] Then, at time t6, at the timing when the shutter electrode 20 stops
moving, the power supply voltage on the power supply line 7 becomes a
level of Vrelease3 (e.g., 15V). As a result, the potential difference
between the shutter electrode 20 and the control electrode on the high
voltage side is decreased from 25V to 15V. At this point, the shutter
electrode 20 is already at a stop. Therefore, there is no influence on
the shutter characteristics even though the applied voltage is decreased.

[0108] Now, with reference to FIG. 8, an operation of the pixel circuit of
the movable shutter-type image display device in this example in the
state of "polarity inversion: shutter=high voltage" will be described. In
FIG. 8, the shutter control voltage on the shutter voltage line 11 is at
a level of Vdrive.

[0109] Until time t1, the scanning line 10 is sequentially supplied with
scanning voltages and an image signal is written in the storage
capacitance 4.

[0110] Next, at time t1, the power supply voltage on the power supply line
12 becomes from a level of Vrelease4 (e.g., 10V) to 0V, and the power
supply voltage on the power supply line 7 becomes from a level of Vdrive
(e.g., 25V) to 0V.

[0111] Next, at time t2, the transfer control signal on the update line 8
becomes H level, and thus the signal transfer switch 13 is turned ON. As
a result, a signal is input to the SRAM circuit formed of the p-type MOS
transistors 2 and 14 and the n-type MOS transistors 3 and 15.

[0112] At time t3, the power supply voltage on the power supply line 7 is
raised to a level of Vlatch, and thus an image signal is latched by the
SRAM circuit.

[0113] Then, at time t4, the transfer control signal on the update line 8
becomes L level, and thus the signal transfer switch 13 is turned OFF.

[0114] At time t5, the power supply voltage on the power supply line 7 is
raised to a level of Vdrive (e.g., 25V), and thus the shutter electrode
20 is driven.

[0115] In an initial state, the shutter electrode 20 is in contact with
either the control electrode 21 or 22. At time t5, the shutter electrode
20 starts moving toward either the control electrode 21 or 22. At this
point, the shutter electrode 20 is supplied with a Vdrive voltage (e.g.,
25V). The control electrode on the high voltage side is supplied with a
Vdrive voltage (e.g., 25V), whereas the control electrode on the low
voltage side is supplied with a voltage of 0V.

[0116] Then, at time t6, at the timing when the shutter electrode 20 stops
moving, the power supply voltage on the power supply line 12 becomes a
level of Vrelease4 (e.g., 10V). As a result, the potential difference
between the shutter electrode 20 and the control electrode on the low
voltage side is decreased from 25V to 10V. At this point, the shutter
electrode 20 is already at a stop. Therefore, there is no influence on
the shutter characteristics even though the applied voltage is decreased.

[0117] In this example, the shutter control voltage on the shutter voltage
line 11 can be of two values as in the conventional art. This provides an
advantage that the structure of the control line driving circuit 26 can
be easily simplified.

Example 3

[0118] In Example 3 according to the present invention, the present
invention is applied to the conventional movable shutter-type image
display device shown in FIG. 16.

[0119] FIG. 9 is a circuit diagram showing a pixel circuit of a movable
shutter-type image display device in this example, which is the same as
the conventional pixel circuit of the movable shutter-type image display
device shown in FIG. 16.

[0121] FIG. 10 is a block diagram showing a schematic structure of the
movable shutter-type image display device in this example.

[0122] Above the pixel circuits 63 arrayed in a matrix, an image signal
voltage write circuit 24 is shown. To the left of the pixel circuits 63,
a scanning circuit 25 is shown. Below the pixel circuits 63, a control
electrode driving circuit 76 is shown.

[0123] In the movable shutter-type image display device shown in FIG. 10,
a plurality of the pixel circuits 63 shown in FIG. 9 are arrayed
two-dimensionally, and each pixel circuit 63 acts as a pixel. A scanning
line 60 is provided for each row and is connected to the scanning circuit
25.

[0124] The signal line 56 is provided for each column and is connected to
the image signal voltage write circuit 24. The pMOS gate voltage line 57,
the positive voltage line 58, the control electrode voltage line 59, the
shutter voltage line 61, the nMOS source voltage line 62, and the cascode
gate voltage line 67 are provided commonly to the pixels, and are
connected to a control electrode driving circuit 76.

[0125] FIG. 11 and FIG. 12 are each a timing diagram of the movable
shutter-type image display device in this example according to the
present invention. In FIG. 11 and FIG. 12, regarding a shutter control
voltage on the shutter voltage line (shutter line) 61, a scanning voltage
on the scanning line (gate line) 60, a control voltage on the control
electrode voltage line (global line) 59, a reset voltage on the pMOS gate
voltage line (reset line) 57, a power supply voltage on the nMOS source
voltage line (low line) 62, and a voltage to be applied to the control
electrode 22, the horizontal axis represents the time and the vertical
axis represents the level of the voltage.

[0126] First, with reference to FIG. 11, an operation of the pixel circuit
of the movable shutter-type image display device in this example in the
state of "polarity inversion: shutter=low voltage" will be described. In
FIG. 11, the shutter control voltage on the shutter voltage line 61 is
0V.

[0127] Until time t11, the scanning line 60 is sequentially supplied with
scanning voltages and an image signal is written in the storage
capacitance 54.

[0128] Next, at time t11, the shutter control voltage on the shutter
voltage line 61 becomes from a level of Vrelease1 (e.g., 10V) to 0V. The
control voltage on the control electrode voltage line 59 becomes from a
level of Vdrive (e.g., 25V) to 0V. The reset voltage on the pMOS gate
voltage line (reset line) 57 becomes from a level of Vdrive to 0V.

[0129] As a result, the potential difference between the control electrode
21 and the shutter electrode 20 becomes 0V, and a Vdrive voltage is
applied to the control electrode 22 via the p-type MOS transistor 52.
Therefore, the shutter electrode 20 moves toward the control electrode
22. The positive voltage line 58 is always supplied with a Vdrive
voltage.

[0130] Next, at time t12, the reset voltage on the pMOS gate voltage line
57 becomes from 0V to a level of Vdrive, and the voltage on the nMOS
source voltage line 62 becomes from a level of VM (e.g., 5V) to 0V.

When the voltage on the nMOS source voltage line 62 becomes 0V, in the
case where the storage capacitance 54 stores an image signal of 5V, the
n-type MOS transistor 53 is turned ON, and a voltage of 0V is applied to
the control electrode 22. In the case where the storage capacitance 54
stores an image signal of 0V, the n-type MOS transistor 53 is not turned
ON. Thus, the control electrode 22 is kept supplied with the Vdrive
voltage.

[0131] When the n-type MOS transistor 53 is turned ON and a voltage of 0V
is applied to the control electrode 22, the shutter electrode 20, which
has been moved toward the control electrode 22, moves to an intermediate
position.

[0132] At time t13, the control voltage on the control electrode voltage
line 59 becomes from 0V to a level of Vdrive, and the voltage on the nMOS
source voltage line 62 becomes from 0 V to a level of VM.

[0133] When the control voltage on the control electrode voltage line 59
becomes the level of Vdrive at time t13, the shutter electrode 20, which
has been moved to the intermediate position during the period from time
t12 to time t13, moves toward the control electrode 21.

[0134] Then, at time t14, at the timing when the shutter electrode 20
stops moving, the shutter control voltage on the shutter voltage line 61
becomes from 0V to a level of Vrelease1. As a result, the potential
difference between the control electrode on the high voltage side and the
shutter electrode 20 is decreased from 25V to 15V. At this point, the
shutter electrode 20 is already at a stop. Therefore, there is no
influence on the shutter characteristics even though the applied voltage
is decreased.

[0135] Now, with reference to FIG. 12, an operation of the pixel circuit
of the movable shutter-type image display device in this example in the
state of "polarity inversion: shutter=high voltage" will be described. In
FIG. 12, the shutter control voltage on the shutter voltage line 61 is at
a level of Vdrive.

[0136] Until time t11, the scanning line (gate line) 60 is sequentially
supplied with scanning voltages and an image signal is written in the
storage capacitance 54.

[0137] Next, at time t11, the shutter control voltage on the shutter
voltage line 61 becomes from a level of Vrelease2 (e.g., 15V) to a level
of Vdrive (e.g., 25V). The control voltage on the control electrode
voltage line (global line) 59 becomes from 0V to a level of Vdrive (e.g.,
25V). The reset voltage on the pMOS gate voltage line (reset line) 57
becomes from a level of Vdrive to 0V.

[0138] As a result, the potential difference between the control electrode
21 and the shutter electrode 20 becomes 0 V, and a Vdrive voltage is
applied to the control electrode 22 via the p-type MOS transistor 52.
Therefore, the shutter electrode 20 moves to an intermediate position.

[0139] At time t12, the reset voltage on the pMOS gate voltage line 57
becomes from 0V to a level of Vdrive, and the voltage on the nMOS source
voltage line (low line) 62 becomes from a level of VM (e.g., 5V) to 0V.

[0140] When the voltage on the nMOS source voltage line 62 becomes 0V, in
the case where the storage capacitance 54 stores an image signal of 5V,
the n-type MOS transistor 53 is turned ON, and a voltage of 0V is applied
to the control electrode 22. In the case where the storage capacitance 54
stores an image signal of 0V, the n-type MOS transistor 53 is not turned
ON. Thus, the control electrode 22 is kept supplied with the Vdrive
voltage.

[0141] When the n-type MOS transistor 53 is turned ON and a voltage of 0 V
is applied to the control electrode 22, the shutter electrode 20 moves
toward the control electrode 22.

[0142] At time t13, the control voltage on the control electrode voltage
line 59 becomes from a level of Vdrive to 0V, and the voltage on the nMOS
source voltage line 62 becomes from 0V to a level of VM.

[0143] When the control voltage on the control electrode voltage line 59
becomes 0V at time t13, the shutter electrode 20, which has been moved to
the intermediate position during the period from time t12 to time t13,
moves toward the control electrode 21.

[0144] Then, at time t14, at the timing when the shutter electrode 20
stops moving, the shutter control voltage on the shutter voltage line 61
becomes from a level of Vdrive to a level of Vrelease2. As a result, the
potential difference between the shutter electrode 20 and the control
electrode on the low voltage side is decreased from 25V to 15V. At this
point, the shutter electrode 20 is already at a stop. Therefore, there is
no influence on the shutter characteristics even though the applied
voltage is decreased.

[0145] A comparison between the timing diagram of FIG. 12 and timing
diagram of FIG. 11 shows that the high/low relationship of the shutter
control voltage on the shutter voltage line 61 and the control voltage on
the control electrode voltage line 59 is opposite to each other, and the
voltage applied to the control electrode 22 is different. However, the
basic operating principle is the same.

[0146] The timing at which the shutter electrode 20 operates is different
between FIG. 11 and FIG. 12, and the timing for obtaining a sufficient
operation time is optimized. Therefore, in FIG. 11, the period between
time 11 and time 12 is long; and in FIG. 12, the period between time 12
and time 13 is long.

[0147] This example provides an advantage that the number of MOS
transistors required in the pixel circuit 63 can be decreased.

Example 4

[0148] A movable shutter-type image display device and a pixel circuit in
this example have substantially the same structure as that in Example 3
described above, and will not be described again.

[0149] FIG. 13 and FIG. 14 are each a timing diagram of the movable
shutter-type image display device in this example. FIG. 13 and FIG. 14
respectively correspond to FIG. 11 and FIG. 12 described above. In FIG.
13 and FIG. 14, regarding the shutter control voltage on the shutter
voltage line (shutter line) 61, the scanning voltage on the scanning line
(gate line) 60, the control signal on the control electrode voltage line
(global line) 59, the reset voltage on the pMOS gate voltage line (reset
line) 57, the power supply voltage on the nMOS source voltage line (low
line) 62, and the voltage to be applied to the control electrode 22, the
horizontal axis represents the time and the vertical axis represents the
level of the voltage.

[0150] In FIG. 13 and FIG. 14, the control voltage on the control
electrode voltage line 59, instead of the shutter control voltage on the
shutter voltage line 61, is decreased in the middle from a level of
Vdrive to a level of Vrelease1 or a level of Vrelease2.

[0151] First, with reference to FIG. 13, an operation of the pixel circuit
of the movable shutter-type image display device in this example in the
state of "polarity inversion: shutter=low voltage" will be described. In
FIG. 13, the shutter control voltage on the shutter voltage line 61 is
0V.

[0152] Until time t11, the scanning line 60 is sequentially supplied with
scanning voltages and an image signal is written in the storage
capacitance 54.

[0153] Next, at time t11, the control voltage on the control electrode
voltage line (global line) 59 becomes from a level of Vrelease2 (e.g.,
15V) to 0V, and the reset voltage on the pMOS gate voltage line (reset
line) 57 becomes from a level of Vdrive to 0V.

[0154] As a result, the potential difference between the control electrode
21 and the shutter electrode 20 becomes 0V, and a Vdrive voltage is
applied to the control electrode 22 via the p-type MOS transistor 52.
Therefore, the shutter electrode 20 moves toward the control electrode
22.

[0155] At time t12, the reset voltage on the pMOS gate voltage line 57
becomes from 0V to a level of Vdrive, and the voltage on the nMOS source
voltage line 62 becomes from a level of VM (e.g., 5V) to 0V.

[0156] When the voltage on the nMOS source voltage line 62 becomes 0V, in
the case where the storage capacitance 54 stores an image signal of 5V,
the n-type MOS transistor 53 is turned ON, and a voltage of 0V is applied
to the control electrode 22. In the case where the storage capacitance 54
stores an image signal of 0V, the n-type MOS transistor 53 is not turned
ON. Thus, the control electrode 22 is kept supplied with the Vdrive
voltage.

[0157] When the n-type MOS transistor 53 is turned ON and a voltage of 0V
is applied to the control electrode 22, the shutter electrode 20, which
has been moved toward the control electrode 22, moves to an intermediate
position.

[0158] At time t13, the control voltage on the control electrode voltage
line 59 becomes from 0V to a level of Vdrive, and the voltage on the nMOS
source voltage line 62 becomes from 0 V to a level of VM.

[0159] When the control voltage on the control electrode voltage line 59
becomes the level of Vdrive at time t13, the shutter electrode 20, which
has been moved to the intermediate position during the period from time
t12 to time t13, moves toward the control electrode 21.

[0160] Then, at time t14, at the timing when the shutter electrode 20
stops moving, the shutter control voltage on the shutter voltage line 61
becomes from 0V to a level of Vrelease2. As a result, the potential
difference between the shutter electrode 20 and the control electrode 21
is decreased from 25V to 15V. At this point, the shutter electrode 20 is
already at a stop. Therefore, there is no influence on the shutter
characteristics even though the applied voltage is decreased.

[0161] Now, with reference to FIG. 14, an operation of the pixel circuit
of the movable shutter-type image display device in this example in the
state of "polarity inversion: shutter=high voltage" will be described. In
FIG. 14, the shutter control voltage on the shutter voltage line (shutter
line) 61 is at a level of Vdrive.

[0162] Until time t11, the scanning line (gate line) 60 is sequentially
supplied with scanning voltages and an image signal is written in the
storage capacitance 54.

[0163] Next, at time t11, the control voltage on the control electrode
voltage line (global line) 59 becomes from a level of Vrelease1 (e.g.,
10V) to a level of Vdrive (e.g., 25V), and the reset voltage on the pMOS
gate voltage line (reset line) 57 becomes from a level of Vdrive to 0V.

[0164] As a result, the potential difference between the control electrode
21 and the shutter electrode 20 becomes 0V, and a Vdrive voltage is
applied to the control electrode 22 via the p-type MOS transistor 52.
Therefore, the shutter electrode 20 moves to an intermediate position.

[0165] At time t12, the reset voltage on the pMOS gate voltage line 57
becomes from 0V to a level of Vdrive, and the voltage on the nMOS source
voltage line (low line) 62 becomes from a level of VM (e.g., 5V) to 0V.

[0166] When the voltage on the nMOS source voltage line 62 becomes 0V, in
the case where the storage capacitance 54 stores an image signal of 5 V,
the n-type MOS transistor 53 is turned ON, and a voltage of 0V is applied
to the control electrode 22. In the case where the storage capacitance 54
stores an image signal of 0V, the n-type MOS transistor 53 is not turned
ON. Thus, the control electrode 22 is kept supplied with the Vdrive
voltage.

[0167] When the n-type MOS transistor 53 is turned ON and a voltage of 0V
is applied to the control electrode 22, the shutter electrode 20 moves
toward the control electrode 22.

[0168] At time t13, the control voltage on the control electrode voltage
line 59 becomes from a level of Vdrive to 0 V, and the voltage on the
nMOS source voltage line 62 becomes from 0 V to a level of VM.

[0169] When the control voltage on the control electrode voltage line 59
becomes 0 V at time t13, the shutter electrode 20, which has been moved
to the intermediate position during the period from time t12 to time t13,
moves toward the control electrode 21.

[0170] Then, at time t14, at the timing when the shutter electrode 20
stops moving, the shutter control voltage on the shutter voltage line 61
becomes from a level of Vdrive to a level of Vrelease1. As a result, the
potential difference between the shutter electrode 20 and the control
electrode 21 is decreased from 25V to 15V. At this point, the shutter
electrode 20 is already at a stop. Therefore, there is no influence on
the shutter characteristics even though the applied voltage is decreased.

[0171] In this example, the potential difference from the shutter
electrode 20 is only the control electrode 21. Instead of the shutter
voltage line 61 which is connected to the storage capacitance and has a
large load capacitance, the control electrode voltage line 59 drives the
shutter electrode 20 with four values of voltage. This provides an
advantage that the driving capacitance is small and thus the structure of
the control electrode driving circuit 26 can be easily simplified.

Example 5

[0172] FIG. 15 is a block diagram showing a schematic structure of an
internet image display device 150 which uses a movable shutter-type image
display device in Example 5 according to the present invention.

[0173] Hereinafter, with reference to FIG. 15, the internet image display
device 150 in Example 5 will be described.

[0174] To a wireless interface (I/F) circuit 152, compressed image data or
the like is input as wireless data from outside. An output of the
wireless I/F circuit 152 is connected to a data bus 158 via an I/O
(input/output) circuit 153.

[0175] The data bus 158 is also connected to a microprocessor (MPU) 154, a
display panel controller 156, a frame memory 157 and the like.

[0176] An output of the display panel controller 156 is connected to a
display device 151 which uses a mechanical shutter. The Internet image
display device 150 also includes a power supply 159.

[0177] The display device 151 using the mechanical shutter has
substantially the same structure as, and performs substantially the same
operation as, those in Example 1 described above, and thus an internal
structure and operation will thereof not be described.

[0178] Hereinafter, an operation of the internet image display device in
Example 5 will be described.

[0179] First, the wireless I/O circuit 152 receives compressed image data
from outside in compliance with an instruction, and transfers the image
data to the microprocessor 154 and the frame memory 157 via the I/O
circuit 153.

[0180] Upon receiving an instruction from the user, the microprocessor 154
drives the entirety of the internet image display device 150 when
necessary to decode the compressed image data, process signals and
display information. The image data processed here can be temporarily
stored on the frame memory 157.

[0181] When the microprocessor 154 issues an instruction to display, the
image data is input from the frame memory 157 to the display device 151
via the display panel controller 154 in compliance with the instruction.
The display device 151 displays the input image data in real time.

[0182] At the same time, the display panel controller 156 also controls
output of prescribed timing pulses required to display the image.

[0183] As described in Example 1, the display device 151 uses these
signals to display the input image data in real time. The power supply
159 includes a secondary cell, which supplies power for driving the
entirety of the Internet image display device 150.

[0184] According to this example, the internet image display device 150
capable of providing high quality display with small power consumption
can be provided at low cost.

[0185] In this example, the display device 151 as described in Example 1
is used as an image display device. Obviously, any of various display
devices described in other examples is usable.

[0186] Needless to say, in such a case, the timing pulses output by the
display panel controller 156 need to be changed slightly.

[0187] In the above description, n-type polycrystalline silicon thin film
transistors are used. Alternatively, amorphous silicon thin film
transistors, which are obtained with no need of crystallization and thus
can be produced by a low cost process, may be usable.

[0188] As described above, in this example, until the shutter electrode 20
contacts either the control electrode 21 or the control electrode 22, the
potential difference between the voltages applied to the electrodes is
25V as by the conventional art. After the electrodes contact each other,
the potential difference between the voltages applied to the electrodes
is decreased to 15V.

[0189] Owing to this, the amount of trapped electrons (charges) caused by
a leak current can be decreased significantly. As a result, the control
fault of the mechanical shutter can be alleviated, and the life of the
display device can be extended significantly.

[0190] The invention made by the present inventor has been described by
way of examples. The present invention is not limited to the
above-provided examples and may be modified in any of various manners
without departing from the scope of the gist of the invention.

[0191] Effects provided by representative subject matter of the invention
disclosed in this application are as follows.

[0192] According to a movable shutter-type image display device of the
present invention, the amount of trapped electrons (charges) caused by a
leak current can be decreased significantly. As a result, the control
fault of the mechanical shutter can be alleviated, and the life of the
display device can be extended significantly.